Function

computed (dependentKeys*, func) ComputedDecorator public

Module: @ember/object

Defined in packages/@ember/-internals/metal/lib/computed.ts:880 

import { computed } from '@ember/object';
dependentKeys*
String
Optional dependent keys that trigger this computed property.
func
Function
The computed property function.
returns
ComputedDecorator
property decorator instance

This helper returns a new property descriptor that wraps the passed computed property function. You can use this helper to define properties with native decorator syntax, mixins, or via defineProperty().

Example:

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import { computed, set } from '@ember/object';

class Person {
  constructor() {
    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  @computed('firstName', 'lastName')
  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
}

let client = new Person();

client.fullName; // 'Betty Jones'

set(client, 'lastName', 'Fuller');
client.fullName; // 'Betty Fuller'

Classic Class Example:

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import EmberObject, { computed } from '@ember/object';

let Person = EmberObject.extend({
  init() {
    this._super(...arguments);

    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  fullName: computed('firstName', 'lastName', function() {
    return `${this.get('firstName')} ${this.get('lastName')}`;
  })
});

let client = Person.create();

client.get('fullName'); // 'Betty Jones'

client.set('lastName', 'Fuller');
client.get('fullName'); // 'Betty Fuller'

You can also provide a setter, either directly on the class using native class syntax, or by passing a hash with get and set functions.

Example:

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import { computed, set } from '@ember/object';

class Person {
  constructor() {
    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  @computed('firstName', 'lastName')
  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  set fullName(value) {
    let [firstName, lastName] = value.split(/\s+/);

    set(this, 'firstName', firstName);
    set(this, 'lastName', lastName);

    return value;
  }
}

let client = new Person();

client.fullName; // 'Betty Jones'

set(client, 'lastName', 'Fuller');
client.fullName; // 'Betty Fuller'

Classic Class Example:

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import EmberObject, { computed } from '@ember/object';

let Person = EmberObject.extend({
  init() {
    this._super(...arguments);

    this.firstName = 'Betty';
    this.lastName = 'Jones';
  },

  fullName: computed('firstName', 'lastName', {
    get(key) {
      return `${this.get('firstName')} ${this.get('lastName')}`;
    },
    set(key, value) {
      let [firstName, lastName] = value.split(/\s+/);
      this.setProperties({ firstName, lastName });
      return value;
    }
  })
});

let client = Person.create();
client.get('firstName'); // 'Betty'

client.set('fullName', 'Carroll Fuller');
client.get('firstName'); // 'Carroll'

When passed as an argument, the set function should accept two parameters, key and value. The value returned from set will be the new value of the property.

Note: This is the preferred way to define computed properties when writing third-party libraries that depend on or use Ember, since there is no guarantee that the user will have prototype Extensions enabled.

The alternative syntax, with prototype extensions, might look like:

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fullName: function() {
  return this.get('firstName') + ' ' + this.get('lastName');
}.property('firstName', 'lastName')

This form does not work with native decorators.